WASHINGTON — The Defense Department has farmed out to a private company much of the criminal investigation and trials of the men accused of plotting the 9/11 attacks on the World Trade Center and the Pentagon, according to federal records and sources affiliated with the trials who spoke to BuzzFeed News.

What’s more, the government has hired the same firm, SRA International, to serve both the prosecution and defense teams, sparking concerns of a conflict of interest that could undermine the integrity of one of the most significant terrorism cases in modern history.

“Where did these people come from; how did they get selected?" asked David Nevin, a lawyer for alleged 9/11 mastermind Khalid Sheikh Mohammed. "I have no idea. And that’s a problem, to say the least.”

The role of contractors in the Gitmo investigations raises questions about accountability at the notoriously secretive war court.

“It does surprise me,” Laura Dickinson, a professor of national security law at George Washington University, said of contracting out a major terrorism investigation. “It raises questions about who is running the investigation. The fact that there is so little transparency raises a red flag because we can’t evaluate if there are adequate accountability measures in place.”

The central role that SRA, a Virginia-based security logistics contracting firm, plays in staffing the prosecution and defense at GITMO has not been previously reported. BuzzFeed News obtained a contracting document dated November 2015, in which the Pentagon justifies using SRA and explains how much the government relies on the company.

Haraz Ghanbari / ASSOCIATED PRESS

A view outside the detention facility at Guantanamo Bay, Cuba.

In the document, the government calls the SRA contractors “vital” — so much so that if they left it would “severely disrupt” the already ​strained judicial proceedings.

The Defense Department has paid SRA almost $39 million over the last five years, U.S. government contracting records show, for the cases of just seven accused terrorists — those charged in the 9/11 attacks and two others charged in the 2000 bombing of the USS Cole off Yemen.

SRA has supplied roughly 45 investigators, intelligence analysts, and others to both the prosecution and defense teams at the military commissions, which are trying the cases at the Guantanamo Bay Naval Base in Cuba. About a fifth of the total military commission staff are SRA contractors, a Defense Department spokesperson said. And the firm’s “proprietary software,” records show, is used to process the evidence in the case.

SRA declined to comment for this story. The Defense Department defended its use of the firm, saying it is critical to the “continuity” of the Guantanamo judicial proceedings, where military personnel rotate through every two to three years.

“All contractors work for OMC personnel who oversee their day-to-day work,” said Cmdr. Gary Ross, a Pentagon spokesman for the Office of Military Commissions.

“They are held to the highest standards of conduct and held accountable to the requirements outlined in the contracts.”

The trials of the alleged 9/11 plotters and two other military commissions defendants have been mired in controversy since their first gavel more than a decade ago. The cases have been stymied by allegations of torture of the defendants at the hands of the CIA, alleged manipulation of defense teams by federal law enforcement, and continued questions over transparency at the war court. Defense lawyers say a trial by 2020 would be “optimistic.”

The widespread use of contractors throughout Washington’s sweeping defense apparatus has been a cause of both fascination and concern. Contractors aren’t beholden to the same transparency standards as the public, government operations they help supplement.

“Some categories of privatization have received scrutiny,” said Dickinson. “There are these other areas in the dark corners of our military and security establishment where contractors are working under the radar and the public doesn’t even know that they’re there.”

The SRA contract played a major role in one of the court’s more recent imbroglios; an SRA security officer assigned to the defense team of a Guantanamo inmate told his employer in 2014 that federal agents had asked him to spy on the very team he was supposed to be helping.

According to the 2015 contracting document, SRA contractors assist both prosecution and defense teams in “all aspects of pre-trial investigation.” Analysts provided by SRA are responsible for combing through dozens of government databases and federal investigation records, interviews, and evidence associated with military commissions cases. They “develop leads for investigative activity or further investigative/data analysis.”

“SRA employees have helped gather evidence and intelligence from all over the world.” And they “have been present for hundreds of interviews with potential witnesses.” They “shall identify additional prosecution and defense witness.”

The Office of Military Commissions awarded its first contract to SRA in 2007, according to records and a former contractor. That first contract was initially narrow in scope, one former contractor said. But it quickly exploded.

“It started out at like six or eight people. And within the first year it was up to 18 ... because of the defense counsel. That’s where the vast majority of the steady growth came from,” the former contractor said, requesting anonymity to discuss the sensitive arrangement.

It is unclear how SRA maintains a clear separation between defense and prosecution staff when it provides staff to both teams. Another former contractor with SRA says that personnel who worked for the defense or prosecution teams were strictly walled off from the opposite side.

“There’s no cross pollination between the two,” said Gary Edgington, a former SRA contract investigator with the Military Commissions. “We did not interact at all because of the rules of due process.”

But Nevin, the lawyer, says there’s a glaring conflict that can’t be resolved if both teams come from the same company. “The fundamental problem is that you’re having defense teams formed by an entity that you don’t control. ... If nothing else, if you had the people coming to you from completely separate sources, you might have a higher degree of confidence that there wasn’t any overlap there.”

(This story has been corrected to reflect that Gary Ross's rank is commander, not lieutenant commander.)

Aram Roston is an investigative reporter for BuzzFeed News and is based in Washington, DC. His secure PGP fingerprint is D861 374F D725 4F61 39C0 08F1 4575 134B 09D9 B28D